Discharge lamp lighting apparatus and lamp apparatus

ABSTRACT

The discharge lamp lighting apparatus has a step-up/step-down converter  3  comprising a transformer  3   a , a first switching element  3   b  serially connected to the transformer  3   a  on a side of a commercial ac power source  1,  and a first diode  3   c  and a first capacitor  3   d  connected to the transformer  3   a  on the load side; zero-cross detection means  10  for detecting the zero-cross of voltage of the commercial ac power source  1;  a supplemental power circuit  4  comprising a second diode  4   a  connected to the junction between the transformer  3   a  and the first switching element  3   b , a second capacitor  4   c  for charging electric power stored in the coil of the transformer  3   a  on a side of the commercial ac power source  1  via the second diode  4   a , and a second switching element  4   b , a third diode  4   f  and an inductance  4   e  through which the energy charged in the second capacitor  4   c  is supplied to the discharge lamp  8;  and a control circuit  9  that operates the second switching element  4   b  in the supplemental power means  4  based on the output from the voltage zero-cross detection means  10  during a predetermined period of time around the zero-cross.

FIELD OF THE INVENTION

[0001] This invention relates to a discharge lamp lighting apparatusthat is powered by the commercial ac power source and lights updischarge lamps at high power factors.

BACKGROUND OF THE PRESENT INVENTION

[0002]FIG. 6 illustrates a circuit configuration of a prior artdischarge lamp lighting apparatus disclosed in Japanese Patent Laid-OpenPublication No. Hei. 9-45490. In this figure, denoted 1 is a commercialac power source, 42 rectifier circuit, 43 step-up inverter, 44 step-downinverter, 45 rectangular wave circuit, 46 starter circuit, 8 dischargelamp, 48 step-up inverter control circuit, 49 step-down inverter controlcircuit, 50 rectangular wave control circuit, and 11 controlled powersource circuit.

[0003] In the discharge lamp lighting apparatus of this configuration,the controlled power source circuit 11 generates controlled power whenthe commercial power source 1 is supplied, and then the step-up invertercontrol circuit 48, the step-down inverter control circuit 49 and therectangular wave control circuit 50 initiate operation.

[0004] The step-up inverter 43 converts an output, which is made byrectifying ac voltage provided by the commercial power source 1 in therectifier circuit 42, into a predetermined dc voltage. In this time, thestep-up inverter control circuit 48 corrects the waveform distortion ofthe input current supplied to the step-up inverter 43 and controls thestep-up inverter 43 so that the input power factor becomes almost 100%.

[0005] The step-down inverter 44 is a DC-to-DC converter that convertsthe dc voltage provided by the step-up inverter 43 into another dcvoltage. The step-down inverter control circuit 49 controls the outputvoltage of the step-down inverter 44 so that the current running throughthe discharge lamp 8 becomes a predetermined current.

[0006] The rectangular wave circuit 45 converts the dc voltage of thestep-down inverter 44 into ac voltage. The rectangular wave controlcircuit 50 controls the rectangular wave circuit 45 so that the currentrunning through the discharge lamp 8 becomes a rectangular alternatingcurrent of a predetermined frequency.

[0007] The starter circuit 46 generates high voltage pulses to start upthe discharge lamp 8.

[0008]FIG. 7 is a block diagram illustrating the conventional lamplighting apparatus, called magnetic type lighting apparatus, wheredenoted 1 is a commercial power source, 51 capacitor, 52 choke coil, 53high voltage pulse generator and 8 discharge lamp. The high voltagepulse generator 53 applies high voltage pulses to the discharge lamp 8.When the discharge lamp 8 lights up, a current runs from the commercialpower source 1 to the discharge lamp 8. The choke coil 52 limits thecurrent flowing to the discharge lamp 8. The capacitor 51 raises thepower factor by improving the lagging in current caused by the chokecoil 52.

[0009] Electric appliances are required to have high power factors inorder to reduce negative effects on power system facilities for the accommercial power. In order to raise the power factor of an electricappliance, it is necessary to convert ac voltage into dc voltage at highpower factors by the use of a step-up inverter, as shown in the exampleof the prior art. Thus, the discharge lamp lighting apparatus becomeslarge and costly as such a step-up inverter is installed.

[0010] On the order hand, it is possible, as shown in FIG. 7, to controlthe current running through the discharge lamp by the use of a chokecoil of large inductance. However, the employment of a large choke coilleads to a large lamp lighting apparatus. In addition, as shown in FIG.8(a), since the discharge lamp current presents the same sinusoidal waveas that of the commercial ac voltage of the commercial power source, theperiod of time when the discharge lamp current is near zero becomeslong. Then as shown in FIG. 8(b), restriking voltage appears when thedischarge lamp current is low. The occurrence of restriking voltageleads to turn-off of the discharge lamp and lowers illuminationefficiency.

DISCLOSURE OF THE INVENTION

[0011] It is, therefore, the object of this invention to provide aninexpensive, small, high power factor discharge lamp lighting apparatusthat can reduce the generation of restriking voltage.

[0012] According to a first embodiment of the present invention, in adischarge lamp lighting apparatus for controlling electric powersupplied to the discharge lamp by a step-up/step-down convertercomprising a transformer, a first switching element serially connectedto the transformer on a side of a commercial ac power source, a firstdiode and a first capacitor connected to the transformer on the loadside, the discharge lamp lighting apparatus includes a zero-crossdetection means for detecting the zero-cross of voltage of thecommercial ac power source; a supplemental power circuit comprising asecond diode connected to a junction between the transformer and thefirst switching element, a second capacitor for charging energy storedin the coil of the transformer on a side of the commercial ac powersource via the second diode, and a second switching element, a thirddiode and an inductance through which the energy charged in the secondcapacitor is supplied to the discharge lamp; and a control circuit thatcalculates the voltage cycle of the commercial ac power source based onthe output from the zero-cross detection means and then operates thesecond switching element in the supplemental power circuit at a highfrequency during a predetermined period of time around the zero-cross.

[0013] As described above, the supplemental power circuit supplieselectric power to the discharge lamp during the period before and afterzero-cross of the commercial ac power source voltage and thus theduration of time the current running through the discharge lamp is zerobecomes short. Therefore, no restriking voltage appears in the dischargelamp, turn-off of the lamp can be prevented, and decrease of theillumination efficiency can be prevented.

[0014] When the first switching device of the step-up/step-downconverter is turned off, the energy stored in the leakage inductance ofthe transformer in the step-up/step-down converter is discharged to thesecond switching element in the power amplification circuit, and then ahigh voltage is applied to the second switching element. Thus it becomespossible to use energy efficiently and raise the conversion rate sincethe high voltage is stored in the capacitor via the diode and thensupplied to the discharge lamp.

[0015] In addition, since the voltage applied to the switching elementcan be lowered, a low withstand voltage switching element can be usedand the system cost is thereby reduced.

[0016] In a second embodiment of the invention, the discharge lamplighting apparatus according to the first embodiment further includescurrent detection means for detecting current running through thedischarge lamp; wherein the control circuit has calculation means forcalculating a target current to be provided to the discharge lamp, thecalculation means provides a constant target current during the periodof time when the second switching element in the supplemental powercircuit is operated at a high frequency and another target current of anarched waveform having peaks at around 90° and 270° of voltage of thecommercial ac power source during the period of time when the secondswitching element is not operated, and the control circuit controls thecurrent running through the discharge lamp detected by the currentdetection means so as to make it equal to the calculated target current.

[0017] As a result, since the input current presents a sinusoidal awaveform similar to that of the commercial ac power source voltage, aninexpensive system with high power factor can be provided without addinga step-up converter for improving power factor.

[0018] According to a third embodiment, in the discharge lamp lightingapparatus set forth in the second embodiment, the target current of anarched waveform having peaks at around 90° and 270° of the commercial acpower source voltage during the period of time when the second switchingelement in the supplemental power circuit is not operated has a waveformof squared sinusoid.

[0019] As a result, the input current supplied from the commercial powersource to the discharge lamp lighting apparatus becomes very similar tothe sine wave. Then the power factor is raised and the harmoniccomponents included in the input current are reduced.

[0020] According to a fourth embodiment of the invention, in thedischarge lamp lighting apparatus set forth in the first embodiment, thecontrol circuit controls the supplemental power circuit to operate onlyduring the period between 45° ahead and 45° behind the zero-cross of thecommercial ac power source voltage or less, controls the constant targetcurrent in the target current so as to make it equal to or less thanhalf the peak value of said target current, and operates the secondswitching element in the supplemental power circuit at the samefrequency and for the same or shorter On-time as that for the firstswitching element in the step-up/step-down converter.

[0021] As a result, the current running through the supplemental powercircuit is reduced to ¼ or less of the current running through thedischarge lamp. Since low current capacity components can be employed inthe supplemental power circuit, the circuit cost can be reduced.

[0022] Moreover, since the switching element in the supplemental powercircuit is operated at the same frequency and for the same orproportional On-time as that of the switching element in thestart-up/step-down converter, distortion in the input current decreaseswhen the supplemental power circuit starts or stops operation. Then theharmonic components included in the input current are reduced.

[0023] Since the switching element in the supplemental power circuit iscontrolled to operate at the same frequency and for the same orproportional On-time as that for the switching element in thestart-up/step-down converter, an additional control circuit thatdetermines the duration of On-time becomes unnecessary and the systemcost can be reduced.

[0024] According to a fifth embodiment of the present invention, in adischarge lamp lighting apparatus for controlling electric powersupplied to the discharge lamp by a step-up/step-down converterincluding a transformer, a first switching element serially connected tothe transformer on a side of the commercial ac power source, a firstdiode and a first capacitor connected to the transformer on the loadside, the discharge lamp lighting apparatus includes zero-crossdetection means for detecting the zero-cross of voltage of thecommercial ac power source; a supplemental power circuit comprising asecond capacitor installed on a side of the commercial ac power sourcewhich is charged via a second diode, a first inductance and the firstswitching element in the step-up/step-down converter, and supplies theenergy stored in the second capacitor to the discharge lamp via a thirddiode, second inductance and second switching element; and a controlcircuit that calculates the voltage frequency of the commercial ac powersource based on the output from the zero-cross detection means and thenoperates the second switching element in the supplemental power circuitat a high frequency during a predetermined period of time around thezero-cross.

[0025] As a result, the supplemental power circuit supplies electricpower to the discharge lamp during the period before and afterzero-cross of the commercial ac power source voltage and thus theduration of time when the current running through the discharge lamp iszero becomes short. Then no restriking voltage appears in the dischargelamp, turn-off of the lamp can be prevented, and decrease of theillumination efficiency can be prevented.

[0026] In addition, since the input current presents a sinusoidalwaveform similar to that of the commercial ac power source voltage, itbecomes possible to raise power factor without adding a step-upconverter for the improvement of power factor and to provide inexpensivedischarge lamp lighting systems.

[0027] According to a sixth embodiment of the invention, the dischargelamp lighting apparatus set forth in the first or fifth embodimentfurther includes current detection means for detecting current runningthrough the discharge lamp; wherein the control circuit switches thesecond switching element in the supplemental power circuit at a highfrequency over the whole cycles of the commercial ac power sourcevoltage until said current detection means detects the current runningthrough the discharge lamp after the discharge lamp lights up.

[0028] As a result, when the discharge lamp starts dielectric breakdowntriggered by high voltage pulses and initiates discharge, thesupplemental power circuit also supplies current to the discharge lamp.Therefore, a sufficient amount of current is provided during thetransition from the unstable discharge state immediately after thedielectric breakdown to stable light-up, and then a smooth start-up isrealized.

[0029] According to a seventh embodiment of the invention, the dischargelamp lighting apparatus set forth in the first or fifth embodimentfurther includes a voltage detection means for detecting the voltage ofthe commercial ac power source; wherein the second switching element inthe supplemental power circuit is switched at a high frequency when thecommercial ac power source voltage is determined to be lower than normalvoltage.

[0030] As a result, even if voltage falls or power supply to thedischarge lamp fails due to a trouble in the commercial ac power source,electric power can be supplied by the supplemental power circuit to thedischarge lamp and then the probability of turn-off of the lamp can belowered even when a trouble arises in the commercial ac power source.

[0031] According to an eight embodiment of the present invention, in adischarge lamp lighting apparatus for controlling electric powersupplied to the discharge lamp by a step-up/step-down converterincluding a transformer, a first switching element serially connected tothe transformer on a side of the commercial ac power source, a firstdiode and a first capacitor connected to the transformer on the loadside, the discharge lamp lighting apparatus includes: zero-crossdetection means for detecting the zero-cross of voltage of thecommercial ac power source; a supplemental power circuit comprising asecond diode connected to the junction between the transformer and thefirst switching element, a second capacitor for charging energy storedin the coil of the transformer on a side of the commercial ac powersource via the second diode, and a second switching element, a thirddiode and an inductance through which the energy stored in the secondcapacitor is supplied to the discharge lamp; and a control circuit thatoperates the second switching element in said supplemental power circuitat the same frequency as that for the first switching element in saidstep-up/step-down converter during an On-time shorter by a predeterminedtime than the On-time of said first switching element, over the wholecycles of the commercial ac power source.

[0032] As a result, even when large current cannot be taken out from thecommercial ac power source during the period around the zero-cross ofthe commercial ac power source voltage, a sufficient current is suppliedto the discharge lamp via the second capacitor and the second switchingelement and the period of time when the current running through thedischarge lamp is zero becomes short. Therefore, no restriking voltageappears in the discharge lamp, turn-off of the lamp can be prevented,and the illumination efficiency does not decrease.

[0033] When the first switching element in the step-up/step-downconverter is turned off, the energy stored in the leakage inductance ofthe transformer in the step-up/step-down converter is discharged as asurge voltage to the second switching element in the power amplificationcircuit. This energy is converted into a switching loss in general.However, since this energy is stored in the capacitor via the seconddiode and then supplied to the discharge lamp in this embodiment, theenergy can be used efficiently and the conversion rate can be increased.

[0034] Further, the surge voltage generated at the first switchingelement is thereby absorbed in the capacitor via the second diode, sothat low withstand voltage switching elements can be used and the systemcost is thereby reduced.

[0035] Since the second switching element is operated at the samefrequency as that of the first switching element during an On-timeshorter by a predetermined time than that of the first switching elementover the whole cycles of the commercial ac power source, it becomespossible to supply current to the discharge lamp via the secondcapacitor and the second switching element to prevent turn-off of thedischarge lamp, even if the commercial ac power source momentarily failsdue to a trouble.

[0036] According to a ninth embodiment of the invention, the dischargelamp lighting apparatus set forth in the eight embodiment furtherincludes current detection means for detecting current running throughthe discharge lamp; wherein the control circuit has calculation meansfor calculating a target current to be provided to the discharge lamp,makes a target current of an arched waveform having peaks at around 90°and 270° of the commercial ac power source voltage almost flat aroundthe zero-cross, and controls the discharge lamp current detected by saidcurrent detection means so as to make it equal to the calculated targetcurrent.

[0037] As a result, since the input current presents a sinusoidalwaveform similar to that of the commercial ac power source voltage, itbecomes possible to raise power factor without adding a step-upconverter for the improvement of power factor and to provide inexpensivedischarge lamp lighting systems.

[0038] The apparatuses described in these first to ninth embodiments ofthe present invention light up discharge lamps, synchronizing with thecommercial ac power source. Thus they are particularly suitable for usein high voltage type discharge lamps such as metal halide lamps, whichare more likely to become unstable in discharge operation upon highfrequency start-up than fluorescent lamps.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a block diagram illustrating a discharge lamp lightingapparatus according to first to fourth and eighth embodiments of thepresent invention.

[0040]FIG. 2 is a diagram illustrating operation waves in the firstembodiment.

[0041]FIG. 3 is a block diagram illustrating a discharge lamp lightingapparatus according to fifth to seventh embodiments of the presentinvention.

[0042]FIG. 4 is a diagram illustrating operation waves in the fifthembodiment.

[0043]FIG. 5 is a diagram illustrating operation waves in the eighthembodiment.

[0044]FIG. 6 is a block diagram illustrating a conventional dischargelamp lighting apparatus.

[0045]FIG. 7 is another block diagram illustrating a conventionaldischarge lamp lighting apparatus.

[0046]FIG. 8 is a diagram illustrating operation waves of a conventionaldischarge lamp lighting apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0047] Embodiment 1

[0048]FIG. 1 is a block diagram illustrating a discharge lamp lightingapparatus according to a first embodiment of the invention, and FIG. 2is a diagram illustrating its operation waveforms. In FIG. 1, denoted 1is the commercial ac power source, 2 diode bridge for the full-waverectification of the commercial ac power, and 3 step-up/step-downconverter for stepping up an stepping down the full-wave rectifiedvoltage, composed of a transformer 3 a, first switching element 3 b,first diode 3 c and first capacitor 3 d. Denoted 4 is a supplementalpower circuit composed of a second diode 4 a, third diode 4 f, diode 4d, second switching element 4 b, second capacitor 4 c and inductance 4e.

[0049] Denoted 8 is a discharge lamp, 5 current detection resistance ascurrent detection means for detecting the current running through thedischarge lamp 8, 6 polarity switching circuit for switching thepolarity of current running through the discharge lamp 8, 7 starterpulse generating circuit for generating high voltage pulses to start upthe discharge lamp 8, 9 control circuit and 10 zero-cross detectionmeans for detecting the zero-cross of voltage of the commercial ac powersource 1.

[0050] Referring now to FIG. 1, the operation thereof is describedbelow. When a commercial ac power source is supplied, the controlcircuit 9 starts to work. The control circuit 9 activates the starterpulse generating circuit 7 and lights up the discharge lamp 8 byapplying high voltage pulses to the discharge lamp 8. Using calculationmeans (not shown), the control means 9 calculates in advance a targetcurrent to be provided to the discharge lamp 8.

[0051] When the discharge lamp 8 lights up, a current runs through thecurrent detection resistance 5. The control circuit 9 reads this currentand controls the step-up/step-down converter 3 with feedback so that thedetected current becomes equal to the target current calculated by thecalculation means of the control circuit 9.

[0052] The first switching element 3 b in the step-up/step-downconverter 3 repeats On/Off operations at a high frequency of severaltens kHz. When the first switching element 3 b is ON, a current runsthrough the transformer 3 a on the primary side and energy is stored inthe transformer 3 a. When the first switching element 3 b turns off, thestored energy is discharged as electric power to the secondary side ofthe transformer 3 b. Since the discharged electric power has a highfrequency of several tens kHz, the included harmonic components areremoved by the first diode 3 c and the first capacitor 3 d, and then theelectric power is supplied to the discharge lamp 8 via the polarityswitching circuit 6.

[0053] If the duration of time when the first switching element 3 b isturned on is prolonged, the energy stored in the transformer 3 aincreases and the output power to the secondary side also increases. Thecontrol circuit 9 prolongs the On-time duration of the first switchingelement 3 b and increases the current provided to the discharge lamp 8if the detected current is lower than the target current. While thedetected current is higher than the target current, the On-time of thefirst switching element 3 b is shortened and the current provided to thedischarge lamp 8 is also reduced. The current running through thedischarge lamp 8 is so controlled as to match with the target current byperforming such operations at high speed.

[0054] The control circuit 9 controls the polarity switching circuit 6,synchronizing with the zero-cross of the commercial ac power sourcedetected by the zero-cross detection means 10. As a result, an accurrent synchronizing with the commercial ac power source runs throughthe discharge lamp 8.

[0055] In the supplemental power circuit 4, electric energy is stored inthe transformer 3 a during the time when the first switching element 3 bin the step-up/step-down converter 3 is turned on, while the storedenergy is discharged as electric power to the secondary side of thetransformer 3 a when the first switching element 3 b is turned off. Atthe same time, electric energy is also stored in the second capacitor 4c via the second diode 4 a in the supplemental power circuit 4.

[0056] Using the calculation means, the control circuit 9 calculates thefrequency of voltage of the commercial ac power source based on thezero-cross of the commercial ac power source voltage detected by thezero-cross detection means 10. Based on the calculated frequency, duringa period from a predetermined time before the zero-cross to apredetermined time after the zero-cross, the control circuit 9 switchesthe switching device 4 b of the supplemental power circuit 4 at a highfrequency and supplies the energy stored in the second capacitor 4 c tothe discharge lamp 8 via the third diode 4 f, inductance 4 e andpolarity switching circuit 6.

[0057] The diode 4 d is a regenerating diode that discharges energystored in the inductance 4 e toward the discharge lamp when the secondswitching element 4 b turns off during the high frequency On/Offoperation of the second switching element 4 b.

[0058] The operation of the supplemental power circuit 4 is furtherdescribed, referring to FIG. 2.

[0059]FIG. 2(a) illustrates the voltage waveform of the commercial acpower source, FIG. 2(b) the waveform of the second switching element 4 bduring its operation, FIG. 2(d) the target current waveform, FIG. 2(c)the waveform of polarity switching, FIG. 2(e) the waveform of currentrunning through the discharge lamp 8, FIG. 2(f) the waveform of thedischarge lamp voltage, and FIG. 2(g) the waveform of the input currentprovided to the discharge lamp lighting apparatus.

[0060] First, the voltage of the waveform shown in FIG. 2(a) is suppliedfrom the commercial ac power source and the second switching element 4 bconducts switching operation at a high frequency during a period betweenthe predetermined times before and after the zero-cross, as shown inFIG. 2(b). On the other hand, the calculation means of the controlcircuit 9 calculates the target current shown in FIG. 2(c). The targetcurrent is set at a direct current during the time when the secondswitching element 4 b is operating at a high frequency, while the targetcurrent is set at an arched current having peaks at 90° and 270° of thewaveform of the commercial ac power source voltage.

[0061] The control circuit 9 reads the current running through thecurrent detection resistance 5 and controls the step-up/step-downconverter 3 and supplemental power circuit 4 with feedback so that thedetected current becomes equal to the target current calculated by thecalculation means of the control circuit 9. The output of thestep-up/step-down converter 3 and the supplemental power circuit 4 ismodified in accordance with the polarity switching wave as shown in FIG.2(d), provided by the polarity switching circuit 6, synchronizing withthe voltage zero-cross of the commercial ac power source 1. This outputcurrent provided to the discharge lamp 8 presents the waveform shown inFIG. 2(e). The duration time when the discharge lamp current is nearzero becomes short because the supplemental power circuit 4 supplieselectric power to the discharge lamp 8 before and after zero-cross asshown in FIG. 2(e). As a result, the discharge lamp voltage presents thevoltage waveform shown in FIG. 2(f) that does not cause restrikingvoltage.

[0062] During the operation of the supplemental power circuit 4, the dcvoltage source of the second capacitor 4 c supplies electric power tothe discharge lamp 8 and at this time the target current is a directcurrent. Consequently, the control circuit 9 drives the first switchingelement 3 b during a fixed On-time and the input current flowing fromthe commercial ac power source to the lighting apparatus presents asinusoid waveform similar to the voltage waveform of the commercial acpower source during the operation of the supplemental power circuit 4.While the supplemental power circuit 4 is not working, the targetcurrent presents an arched waveform having peaks at 90° and 270° thevoltage waveform (or voltage cycle) of the commercial ac power source.Then the input current also presents an arched waveform having peaks at90° and 270° of the commercial ac power source voltage. As a result, theinput current presents a sinusoidal waveform similar to the voltagewaveform of the commercial ac power source, as shown in FIG. 2(g).

[0063] As evident from the waveform of the current running through thedischarge lamp shown in FIG. 2(e) and the waveform of the voltageapplied to the discharge lamp shown in FIG. 2(f), the voltage of thedischarge lamp is kept constant regardless of the current of thedischarge lamp. Now suppose that the discharge lamp voltage is apredetermined constant value, A, and the voltage of the commercial acpower source is given by V° sin θ. If the current flowing from thecommercial ac power source to the discharge lamp lighting apparatus hasto have a waveform of I° sin θ synchronizing with the voltage of thecommercial ac power source, the discharge lamp current should take awaveform expressed by a square of sin θ, as derived from the equation:

V° sin θ×I° sin θ=A×Discharge lamp current.

[0064] Then the power factor improves, because the input current has awaveform of sin θ synchronizing with the commercial ac power sourcevoltage. The waveform of square sin θ is similar to that shown in FIG.2(g).

[0065] As described above, the supplemental power circuit 4 supplieselectric power to the discharge lamp 8 during the period before andafter zero-cross of voltage of the commercial ac power source 1 and thusthe duration of time when the current running through the discharge lamp8 is zero becomes short. Then no restriking voltage of the dischargelamp 8 appears, turn-off of the lamp can be prevented, and decrease ofthe illumination efficiency can be prevented.

[0066] When the first switching element 3 b of the step-up/step-downconverter 3 is turned off, the energy stored in the leakage inductanceof the transformer 3 a of the step-up/step-down converter 3 isdischarged to the supplemental power circuit 4, and then a high voltageis applied to the second switching element 4 b. In most cases, a snubbercircuit composed of capacitors and resistors is employed to convert thishigh voltage into heat for exhaustion. In the present embodiment, it ispossible to use energy efficiently and raise the conversion rate sincethe high voltage is stored in the second capacitor 4 c via the seconddiode 4 a and then supplied to the discharge lamp 8.

[0067] In addition, since the voltage applied to the second switchingelement 4 b can be lowered, low withstand voltage switching elements canbe employed and the system cost is thereby reduced.

[0068] When the supplemental power circuit 4 is operating during theperiod before and after the zero-cross of the commercial ac power sourcevoltage, the commercial ac power source supplies little of power to thedischarge lamp 8 because of the low voltage of the source and the secondcapacitor 4 c of the supplemental power circuit 4 supplies most ofpower. The target current supplied to the discharge lamp 8 during thisperiod is set at the flat portion of the waveform shown in FIG. 2(c).That is, the target current is a constant current during this period.Since the main power source to supply power to the discharge lamp 8 isthe direct current from the capacitor 4 c, the current supplied to thedischarge lamp 8 is made constant by making the control circuit 9 todrive the second switching element 4 b during a fixed On-time. If thefirst switching element 3 b is also driven during the fixed On-time, thecurrent flowing from the commercial ac power source 1 to the lightingapparatus presents a sinusoidal waveform similar to the waveform of thecommercial ac power source voltage. While the supplemental power circuit4 is not working, the target current presents an arched waveform havingpeaks at 90° and 270° of the commercial ac power source voltage. As aresult, the input current presents a sinusoidal waveform similar to thatof the commercial ac power source voltage, and it becomes possible toraise power factor without adding a step-up converter for theimprovement of power factor.

[0069] Besides, while the second switching element 4 b in thesupplemental power circuit 4 is not working, the target current presentsan arched waveform expressed by squared sinusoid having peaks at around90° and 270° of the commercial ac power source voltage and a waveform.Therefore, the input current supplied from the commercial ac powersource 1 to the discharge lamp lighting apparatus becomes very similarto the sine wave. Then the power factor is raised, and the harmoniccomponents included in the input current are reduced.

[0070] Embodiment 2

[0071] Since the block diagram of the discharge lamp lighting apparatusaccording to the second embodiment of the invention is the same as thatof the first embodiment, the second embodiment is explained withreference to FIG. 1.

[0072] In FIG. 1, the operation period of the supplemental power circuit4 is limited to a period between 45° ahead and 45° behind the zero-crossof the commercial ac power source 1 or less, namely a half cycle of thecommercial ac power source or less. Besides, the value of the targetcurrent is set at a half of the peak value of the target current orless.

[0073] In addition, the switching element 4 b in the supplemental powercircuit 4 is controlled so that it operates at the same frequency andfor the same On-time or a few μsec shorter On-time as that of the firstswitching element 3 b in the startup/step-down converter 3.

[0074] Since the operation period of the supplemental power circuit 4 islimited to the period between 45° ahead and 45° behind the zero-cross ofthe commercial ac power source 1 or less, namely a half cycle of thecommercial ac power source or less, and the value of the target currentis set at a half of the peak value of the target current or lower, thecurrent running through the supplemental power circuit is reduced to ¼or less of the current running through the discharge lamp. As a result,low current capacity components can be used in the supplemental powercircuit and the circuit cost is thus reduced.

[0075] Moreover, since the switching element 4 b in the supplementalpower circuit 4 is controlled to operate at the same frequency as thatof the first switching element 3 b in the start-up/step-down converter 3for the same or proportional On-time, distortion in the input currentdecreases which appears when the supplemental power circuit 4 starts orstops operation. Then the harmonic components included in the inputcurrent are reduced and the system cost can be reduced because nocontrol circuit needs to be added for the determination of On-time.

[0076] Embodiment 3

[0077] Since the block diagram of the discharge lamp lighting apparatusaccording to the third embodiment of the invention is the same as thatof the first embodiment shown in FIG. 1, the third embodiment isexplained with reference to FIG. 1.

[0078] The second switching element 4 b in the supplemental powercircuit 4 is switched at a high frequency over whole cycle of thecommercial ac power source, until the starter pulse generating circuit 7applies high voltage pulses to the discharge lamp 8 for lighting up andthe current running through the discharge lamp 8 is detected by thecurrent detection resistance 5.

[0079] When the discharge lamp starts dielectric breakdown triggered byhigh voltage pulses and initiates discharge, the supplemental powercircuit also supplies current to the discharge lamp. Therefore, asufficient amount of current is provided during the transition from theunstable discharging state immediately after the dielectric breakdown tostable light-up, and then a smooth start-up is realized.

[0080] Embodiment 4

[0081] Since the block diagram of the discharge lamp lighting apparatusaccording to the fourth embodiment of the invention is the same as thatof the first embodiment shown in FIG. 1, the fourth embodiment isexplained with reference to FIG. 1.

[0082] The voltage detection means installed in the control circuit 9detects the commercial ac power source voltage. If a decrease from thenormal voltage is detected in the commercial ac power source voltage,the second switching element 4 b in the supplemental power circuit 4 isswitched at a high frequency even when it is out of the predeterminedtime before and after the zero-cross of the commercial ac power sourcevoltage.

[0083] Therefore, even if a trouble arises in the commercial ac powersource, the probability of turn-off of the lamp can be lowered.

[0084] Embodiment 5

[0085]FIG. 3 is a block diagram illustrating the discharge lamp lightingapparatus according to the fifth embodiment of the invention. Referringto FIG. 3, denoted 1 is the commercial ac power source, 2 diode bridgefor the full-wave rectification of the commercial ac power, 3step-up/step-down converter that raises and lowers the full-waverectified voltage, and 4 supplemental power circuit composed of a secondcapacitor 4 c, second diode 4 h, third diode 4 k, first inductance 4 g,second inductance 4 j, and second switching element 4 b. Denoted 8 is adischarge lamp, 5 current detection resistance that detects the currentrunning through the discharge lamp 8, 6 polarity switching circuit thatswitches the polarity of current running through the discharge lamp 8, 7starter pulse generating circuit that generates high voltage pulses tostart up the discharge lamp 8, and 9 control circuit.

[0086] The second capacitor 4 c, second diode 4 h and first inductance 4g constitute charging means for electric charge via the switchingelement 3 b in the step-up/step-down converter 3, while the third diode4 k, second inductance 4 j and second switching element 4 b constitutedischarging means.

[0087] Next, the operation is described with reference to FIG. 3. In thesupplemental power circuit 4, the current flows to the primary side ofthe transformer 3 a when the first switching element 3 b in thestep-up/step-down converter 3 is turned on and then the transformerstores energy. At the same time, a current flows in the second capacitor4 c, second diode 4 h and first inductance 4 g, and then the secondcapacitor 4 c stores electric charge.

[0088] The control circuit 9 detects the zero-cross of the commercial acpower source voltage and measures the interval of the commercial acpower source voltage. Based on the calculated period, the controlcircuit 9 switches the second switching element 4 b at a high frequencyfor a predetermined period before and after the zero-cross in order tosupply the energy stored in the second capacitor 4 c to the primary sideof the transformer 3 a via the second switching element 4 b, third diode4 k and second inductance 4 j.

[0089] The other operations of this circuit are the same as thosedescribed in the first embodiment shown in FIG. 1.

[0090] The operation of the supplemental power circuit 4 is furtherdescribed, referring to FIG. 4.

[0091]FIG. 4(a) illustrates the voltage waveform of the commercial acpower source, FIG. 4(b) the waveform of the second switching element 4 bduring its operation, FIG. 4(c) the target current waveform, FIG. 4(d)the waveform of polarity switching, FIG. 4(e) the waveform of currentrunning through the discharge lamp 8, FIG. 4(f) the waveform of thedischarge lamp voltage and FIG. 4(g) the waveform of the input currentprovided to the discharge lamp lighting apparatus.

[0092] First, the voltage of the waveform shown in FIG. 4(a) is suppliedfrom the commercial ac power source and the second switching device 4 bconducts switching operation at a high frequency during thepredetermined period before and after the zero-cross, as shown in FIG.4(b). On the other hand, the calculation means of the control means 9calculates the target current shown in FIG. 4(c). The target current isa direct current during the time the second switching element 4 b isoperating at a high frequency, while the target current is an archedcurrent having peaks at 90° and 270° of the waveform of the commercialac power source voltage.

[0093] The control circuit 9 reads the current running through thecurrent detection resistance 5 and controls the step-up/step-downconverter 3 and supplemental power circuit 4 with feedback so that thedetected current becomes equal to the target current calculated by thecalculation means of the control circuit 9. The output of thestep-up/step-down converter 3 and the supplemental power circuit 4 isconverted by the polarity switching wave provided by the polarityswitching circuit 6, as shown in FIG. 4(d), synchronizing with thevoltage zero-cross of the commercial ac power source 1. This outputrunning through the discharge lamp 8 presents the waveform shown in FIG.4(e).

[0094] The duration time when the discharge lamp current is near zerobecomes short because the supplemental power circuit 4 supplies electricpower to the discharge lamp 8 before and after zero-cross, as shown inFIG. 4(e). As a result, the discharge lamp voltage presents the voltagewaveform shown in FIG. 4(f) that does not cause restriking voltage.

[0095] During the operation of the supplemental power circuit 4, the dcvoltage source of the second capacitor 4 c supplies power to thedischarge lamp 8 via the step-up/step-down converter 3. Then the inputcurrent flowing from the commercial ac power source to the lightingapparatus becomes close to zero as shown in FIG. 4(g). On the otherhand, during the other periods, the target current is an arch currenthaving peaks at 90° and 270° of the waveform of the commercial ac powersource voltage. Then the input current also presents a sinusoidal wavesimilar to the waveform of the commercial ac power source voltage havingpeaks at 90° and 270° in phase. As is the case with the firstembodiment, if the arched type target current has a waveform of squaredsinusoid, the input current becomes further close to the sinusoidalwave.

[0096] As described above, the supplemental power circuit 4 supplieselectric power to the discharge lamp 8 during the period before andafter zero-cross of the commercial ac power source voltage and thus theduration of time when the current running through the discharge lamp 8is zero becomes short. Therefore, no restriking voltage of the dischargelamp 8 appears, turn-off of the lamp can be prevented, and decrease ofthe illumination efficiency can be prevented.

[0097] In the period before and after zero-cross of the commercial acpower source voltage, the discharge lamp 8 is powered via thestep-up/step-down converter 3 by the direct-current voltage source ofthe capacitor in the supplemental power circuit 4 when the supplementalpower circuit 4 is operating. Therefore, the current flowing from thecommercial ac power source 1 to the discharge lamp 8 becomes zero.However, when the supplemental power circuit 4 is not working, since thetarget current presents an arched waveform having peaks at 90° and 270°of the commercial ac power source voltage, so that the input currentpresents an arched waveform having peaks at 90° and 270° of the waveformof the commercial ac power source voltage. As a result, the inputcurrent presents a sinusoidal waveform similar to that of the commercialac power source voltage. Then it becomes possible to raise power factorwithout adding the step-up converter 3 for the improvement of powerfactor and to provide inexpensive discharge lamp lighting systems.

[0098] Embodiment 6

[0099] Since the block diagram of the discharge lamp lighting apparatusaccording to the sixth embodiment of the invention is the same as thatof the fifth embodiment shown in FIG. 3, the sixth embodiment isexplained with reference to FIG. 3.

[0100] The second switching element 4 b in the supplemental powercircuit 4 is switched at a high frequency over whole cycles of thecommercial ac power source, until the starter pulse generating circuit 7applies high voltage pulses to the discharge lamp 8 for lighting up andthe current running through the discharge lamp 8 is detected by thecurrent detection resistance 5.

[0101] When the discharge lamp starts dielectric breakdown triggered byhigh voltage pulses and initiates discharge, the supplemental powercircuit also supplies current to the discharge lamp. Therefore, asufficient amount of current is provided during the transition from theunstable discharge state immediately after the dielectric breakdown tostable light-up, and then a smooth start-up is realized.

[0102] Embodiment 7

[0103] Since the block diagram of the discharge lamp lighting apparatusaccording to the seventh embodiment of the invention is the same as thatof the fifth embodiment shown in FIG. 3, the seventh embodiment isexplained with FIG. 3.

[0104] The voltage detection means installed in the control circuit 9detects the commercial ac power source voltage. If a decrease from thenormal voltage is detected in the commercial ac power source voltage,the second switching element 4 b in the supplemental power circuit 4 isswitched at a high frequency even when it is out of the predeterminedperiod before and after the zero-cross of the commercial ac power sourcevoltage.

[0105] Then even if a problem arises in the commercial ac power source,the probability of turn-off of the lamp can be decreased.

[0106] Embodiment 8

[0107] Since the block diagram of the discharge lamp lighting apparatusaccording to the eighth embodiment of the invention is the same as thatof the first embodiment shown in FIG. 1, the eighth embodiment isexplained with reference to FIG. 1.

[0108] In the first embodiment, the second switching element 4 b in thesupplemental power circuit 4 is switched at a high frequency during thepredetermined period before and after the zero-cross of the commercialac power source voltage, and during this period the energy stored in thesecond capacitor 4 c is provided to the discharge lamp 8. In the eightembodiment, the second switching element 4 b in the supplemental powercircuit 4 is switched, at the same frequency as the operation frequencyof the first switching element 3 b in the step-up/step-down converter 3,so as to have an On-time shorter by a predetermined time than that ofthe switching element 3 b, over the whole cycle of the commercial acpower source voltage. Then the energy stored in the second capacitor 4 cis supplied to the discharge lamp 8.

[0109] The operation of the supplemental power circuit 4 is described,referring to FIG. 5 that illustrates the operation waveforms.

[0110]FIG. 5(a) illustrates the voltage waveform of the commercial acpower source, FIG. 5(b) the target current waveform, FIG. 5(c) thewaveforms of the switching elements 3 b and 4 b during their On-times,namely FIG. 5(cl) the waveform of the switching element 3 b and FIG. 5(c2) the waveform of the switching element 4 b. FIG. 5(d) illustrates thewaveform of polarity switching, FIG. 5(e) the waveform of currentrunning through the discharge lamp 8, FIG. 5(f) the waveform of thedischarge lamp voltage, and FIG. 5(g) the waveform of the input currentto the discharge lamp lighting apparatus.

[0111] First, the voltage of the waveform shown in FIG. 5(a) is suppliedfrom the commercial ac power source and the calculation means of thecontrol means 9 calculates the target current shown in FIG. 5(b). Thetarget current is a direct current during the period before and afterthe zero-cross of the commercial ac power source voltage, while thetarget current is an arch current having peaks at 90° and 270° of thewaveform of the commercial ac power source voltage.

[0112] The control circuit 9 reads the current running through thecurrent detection resistance 5 and controls the step-up/step-downconverter 3 with feedback so that the detected current becomes equal tothe target current calculated by the calculation means of the controlcircuit 9. Since it is difficult to take out power during the periodaround the zero-cross of the commercial ac power source voltage becauseof the low voltage, the control circuit 9 increase the On-time of theswitching element 3 b as shown in FIG. 5(c 1) to take out necessarypower. At this time, since the On-time of the switching element 4 b isalso increased as shown in FIG. 5(c 2), supplemental power is suppliedto the discharge lamp 8 via the second capacitor 4 c, third diode 4 f,inductance 4 e and polarity switching circuit 6 to make up for theshortage of power supply from the commercial ac power source. Based onthe polarity switching waveform shown in FIG. 5(d), the polarityswitching circuit 6 switches the current running through the dischargelamp 8 as shown in FIG. 5(e).

[0113] A large amount of electric power is required around thezero-cross of the commercial ac power source voltage in order tosuppress the restriking voltage that appears in the discharge lamp 8. Atthis time, since the second capacitor 4 c supplies power to thedischarge lamp 8, the current flowing from the commercial ac powersource to the discharge lamp lighting apparatus decreases and then theinput current waveforms around the zero-cross of the commercial ac powersource voltage are similar to those of the commercial ac power sourcevoltage. During the period of time when the target current is an archedcurrent having peaks at 90° and 270° of the waveform of the commercialac power source voltage, the restriking voltage does not appear, andthen the input current becomes proportional to the discharge lampcurrent. Namely, if the discharge lamp current has an arched waveformhaving peaks at 90° and 270° in phase, the input current also shows anarched type waveform. Therefore, as shown in FIG. 5(g) that illustratesthe input current waveform, the input current has an arched waveformsimilar to the waveform of the commercial ac power source voltage.

[0114] Referring now to an area (A) in FIG. 5(a), if the supply of thecommercial ac power source voltage stops momentarily because of anaccident, the control circuit 9 increases the On-time of the switchingelement 3 b as shown FIG. 5(c 1), trying to take out electric power.Then the On-time of the switching element 4 b is also increased as shownin FIG. 5(c 2), and the second capacitor 4 c provides electric power tothe discharge lamp 8. As a result, the turn-off of the discharge lamp 8is prevented.

1. A discharge lamp lighting apparatus, for controlling electric powersupplied to a discharge lamp by a step-up/step-down converter comprisinga transformer, a first switching element serially connected to thetransformer on a side of a commercial ac power source, and a first diodeand a first capacitor connected to the transformer on a load side, thedischarge lamp lighting apparatus comprising: zero-cross detection meansfor detecting zero-cross of voltage of said commercial ac power source;a supplemental power circuit comprising a second diode connected to ajunction between said transformer and said first switching element, asecond capacitor for charging energy stored in a coil of saidtransformer on a side of said commercial ac power source via said seconddiode, and a second switching element, a third diode and an inductancethrough which the energy charged in the second capacitor is supplied tosaid discharge lamp; and a control circuit that calculates a voltagecycle of said commercial ac power source based on an output from saidzero-cross detection means and then operates said second switchingelement in said supplemental power circuit at a high frequency during apredetermined period of time around the zero-cross.
 2. The dischargelamp lighting apparatus according to claim 1, further comprising currentdetection means for detecting current running through said dischargelamp; wherein said control circuit has calculation means for calculatinga target current to be provided to said discharge lamp, said calculationmeans provides a constant target current during the period of time whenthe second switching element in said supplemental power circuit isoperated at a high frequency and another target current of an archedwaveform having peaks at around 90° and 270° of voltage of saidcommercial ac power source during the period of time when said secondswitching element is not operated, and said control circuit controls thecurrent running through said discharge lamp detected by said currentdetection means so as to make it equal to said calculated targetcurrent.
 3. The discharge lamp lighting apparatus according to claim 2,wherein said target current of an arched waveform having peaks at around90° and 270° of said commercial ac power source voltage during theperiod of time when the second switching element of said supplementalpower circuit is not operated has a waveform of squared sinusoid.
 4. Thedischarge lamp lighting apparatus according to claim 1, wherein saidcontrol circuit controls said supplemental power circuit to operate onlyduring the period between 45° ahead and 45° behind the zero-cross ofsaid commercial ac power source voltage or shorter, controls saidconstant, target current in the target current so as to make it equal toor less than half the peak value of said target current, and operatesthe second switching element in said supplemental power circuit at thesame frequency and for the same or a shorter On-time as that for thefirst switching element in said step-up/step-down converter.
 5. Adischarge lamp lighting apparatus, for controlling electric powersupplied to a discharge lamp by a step-up/step-down converter comprisinga transformer, a first switching element serially connected to thetransformer on a side of a commercial ac power source, and a first diodeand a first capacitor connected to the transformer on a load side, thedischarge lamp lighting apparatus comprising: zero-cross detection meansfor detecting zero-cross of voltage of said commercial ac power source;a supplemental power circuit comprising a second capacitor installed ona side of said commercial ac power source which is charged via a seconddiode, a first inductance and the first switching element in thestep-up/step-down converter, and supplies energy stored in the secondcapacitor to said discharge lamp via a third diode, second inductanceand second switching element; and a control circuit that calculates avoltage cycle of said commercial ac power source based on an output fromsaid zero-cross detection means and then operates said second switchingelement in said supplemental power circuit at a high frequency during apredetermined period of time around the zero-cross.
 6. The dischargelamp lighting apparatus according to claim 1, further comprising currentdetection means for detecting the current running through said dischargelamp; wherein said control circuit switches the second switching elementin said supplemental power circuit at a high frequency over the wholecycles of said commercial ac power source voltage until said currentdetection means detects current running through said discharge lampafter lighting up of said discharge lamp.
 7. The discharge lamp lightingapparatus according to claim 1, further comprising voltage detectionmeans for detecting voltage of said commercial ac power source; whereinsaid second switching element in said supplemental power circuit isswitched at a high frequency when said commercial ac power sourcevoltage is determined to be lower than a normal voltage.
 8. A dischargelamp lighting apparatus, for controlling electric power supplied to adischarge lamp by a step-up/step-down converter comprising atransformer, a first switching element serially connected to saidtransformer on a side of a commercial ac power source, and a first diodeand a first capacitor connected to the transformer on a load side, thedischarge lamp lighting apparatus comprising: zero-cross detection meansfor detecting zero-cross of voltage of said commercial ac power source;a supplemental power circuit comprising a second diode connected to ajunction between said transformer and said first switching element, asecond capacitor for charging energy stored in a coil of saidtransformer on a side of said commercial ac power source via said seconddiode, and a second switching element, a third diode and an inductancethrough which the energy stored in the second capacitor is supplied tosaid discharge lamp; and a control circuit that operates said secondswitching element in said supplemental power circuit at the same highfrequency as that for the first switching element in saidstep-up/step-down converter, with an On-time shorter by a predeterminedtime than the On-time of said first switching element, over whole cyclesof said commercial ac power source.
 9. The discharge lamp lightingapparatus according to claim 8, further comprising current detectionmeans for detecting current running through said discharge lamp; whereinsaid control circuit has calculation means for calculating a targetcurrent to be provided to said discharge lamp to make a target currentof an arched waveform having peaks at around 90° and 270° of saidcommercial ac power source voltage and almost flat portions aroundzero-cross, and controls current running through the discharge lamp,which is detected by said current detection means, so as to make itequal to said calculated target current.
 10. A lamp apparatus having thedischarge lamp lighting apparatus according to claim
 1. 11. Thedischarge lamp lighting apparatus according to claim 5, furthercomprising current detection means for detecting the current runningthrough said discharge lamp; wherein said control circuit switches thesecond switching element in said supplemental power circuit at a highfrequency over the whole cycles of said commercial ac power sourcevoltage until said current detection means detects current runningthrough said discharge lamp after lighting up of said discharge lamp.12. The discharge lamp lighting apparatus according to claim 5, furthercomprising voltage detection means for detecting voltage of saidcommercial ac power source; wherein said second switching element insaid supplemental power circuit is switched at a high frequency whensaid commercial ac power source voltage is determined to be lower than anormal voltage.
 13. A lamp apparatus having the discharge lamp lightingapparatus according to claim
 2. 14. A lamp apparatus having thedischarge lamp lighting apparatus according to claim
 3. 15. A lampapparatus having the discharge lamp lighting apparatus according toclaim
 4. 16. A lamp apparatus having the discharge lamp lightingapparatus according to claim
 5. 17. A lamp apparatus having thedischarge lamp lighting apparatus according to claim
 6. 18. A lampapparatus having the discharge lamp lighting apparatus according toclaim
 7. 19. A lamp apparatus having the discharge lamp lightingapparatus according to claim
 8. 20. A lamp apparatus having thedischarge lamp lighting apparatus according to claim 9.